Mobile mine roof support



Nov. 23, 1965 w. WILKENLOH 3,218,812

MOBILE MINE ROOF SUPPORT Filed May 14, 1962 2 Sheets-Sheet 1 .9 n a MMIY .Q5 .A n a fk# 3 um .lw Nw R P. U J r x T n a. A @HU J .w a RL S nh .aM u, .1 n n ,WH

Nov. 23, 1965 w. wlLKENLol-l MOBILE MINE ROOF SUPPORT 2 Sheets-Sheet 2Filed May 14., 1962 United States Patent Ofi 3,218,812 Patented Nov. 23,1965 .Lice

3,218,812 MOBILE IVHNE ROOF SUPPORT Wilhelm Wilkenloh,Duisburg-Weilheim, Germany, assignor to Rheinstahl Wanheim G.m.b.H.,Duisburg- Wanheim, Germany Filed May 14, 1962, Ser. No. 194,386 Claimspriority, application Germany, May 13, 1961, R 39,332 Claims. (Cl.61-45) The present invention relates to mine roof supports, and moreparticularly to an improved mobile mine roof support which is especiallysuited for use in underground excavations whose floors consist ofcomparatively soft, comminuted or other yieldable material. It is wellknown that the floor contacting elements of a mine roof support oftenpenetrate into the material of the mine floor so that it is ratherditiicult, if not impossible, to rapidly advance the mine roof supportto a new position. Furthermore, it happens rather frequently that thematerial which is separated from the mine face or which drops from themine roof accumulates on the Hoor contacting elements of the mine roofsupport so that it becomes necessary to remove such accumulations ofmaterial before the mine roof support can be moved along the mine door.Finally, the mine oor is frequently uneven, i.e., it has depressions andprotuberances which might reach such dimensions that they prevent thefloor contacting elements from passing thereover when the mine roofsupport is to be shifted toward the mine face. However, the forwardmovement of the mine roof support is normally hindered to a lesserdegree by the unevenness of mine oor than by sinking of the floorcontacting elements at the time the roof engaging cap or caps are insupporting engagement with the mine roof and carry a heavy load of rock,ore or the like.

Accordingly, it is an important object of the present invention toprovide a mobile multi-prop mine roof support which is constructed andassembled in such a way that it can rapidly and conveniently extricateand lift its floor engaging elements prior to advancing along the minefloor.

Another object of the invention is to provide a mine roof support of thejust outlined characteristics whose props, in addition to enabling thecap or caps to become separated from or to move into supportingengagement with the mine roof, may also serve as a means for extricatingand lifting the door engaging elements of the mine roof support beforethe latter is caused to move toward the mine face.

A further object of the present invention is to provide a multi-propmine roof support of the above described type whose cap or caps areconstructed and assembled in such a way that they can support one ormore extensible and contractible props in suspended position as long asat least one prop remains extended to maintain the cap or caps insupporting engagement with the mine roof.

An additional object of my invention is to provide a composite cap for amine roof support Whose component parts are capable of performingmovements with respect to each other so `as to assume optimum supportingpositions when they engage the mine roof but which is still strongenough to support one or more props in suspended position and towithstand the weight of material which might have accumulated on the oorengaging elements of the props, such material normally tending toprevent extraction of the lioor engaging elements when the props arecaused to contract.

Still another object of the invention is to provide a mobile mine roofsupport wherein the control system which regulates the extension andcontraction of the props and/or the forward movement of the mine roofsupport may also serve as a means for regulating the extraction of floorcontacting elements before the mine roof support is caused to advancealong the mine oor.

A concomitant object of the invention is to provide a method ofextracting and lifting the licor engaging lower portions of props in amulti-prop mine roof support.

With the above objects in view, the invention resides in the provisionof a mobile mine roof support which comprises at least two extensibleand contractible pit props each of which has at least two relativelymovable portions including an upper portion and a oor engaging lowerportion; and a one-piece or composite roof engaging cap which isconnected with the upper portions of the props and which is adapted tosupport one of the props in suspended position and to thereby lift therespective floor engaging lower portion above the mine floor when theother prop is extended and causes the cap to supportingly engage themine roof, whereby any depressions formed by the floor engaging portionsmay be iilled in by the operators or are filled automatically byavalanching of the material of which the mine floor consists while thelower portions are alternately lifted above the mine lioor so that,after descending into renewed contact with the mine door, the lowerportions will be located at the general level of the mine floor and willnot hinder forward movements of the mine roof support. The props arealternately suspended on the cap means so that the respective oorengaging lower portions are lifted above the oor and permit filling ofthe depressions if the depressions made by the momentarily lifted lowerportions are of such depth that they could hinder forward movements ofthe mine roof support. If the apparatus comprises two or more pairs ofprops, one or more pairs of props may be suspended simultaneously aslong as the cap remains in supporting engagement with the roof and aslong as the cap is strong enough to maintain two or more props insuspended position.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe 'best understood from the following detailed description of certainspecific embodiments with reference to the accompanying drawings, inwhich:

FIG. l is a side elevational View of a mobile four-prop mine roofsupport which comprises a composite cap and which embodies one form ofmy invention;

FIG. 2 is a top plan view of the mine roof support;

FIG. 3 is a transverse section as seen in the direction of arrows fromthe line III- III of FIG. 2;

FIG. 4 is an enlarged axial section through a pit prop which forms partof the mine roof support shown in FIGS. 1 to 3; and

FIG. 5 is a fragmentary side elevational view of a modified mine roofsupport which comprises a single pair of props and a one-piece roofengaging cap.

Referring now in greater detail to the illustrated embodiments, andfirst to FIGS. l to 3, there is shown a mobile mine roof support whichcomprises four extensible and contractible pit props including twotransversely aligned leading props 1, 2 and two transversely alignedtrailing props 3, 4. Each of these props comprises a tubular lowerportion 5 and a tubular upper portion 6, the former constituting acylinder and the latter constituting a piston rod which extends into andwhich is reciprocable in the respective cylinder. The upper portions 6of the props 1 to 4 are articulately connected with a composite roofengaging cap 7 whose exact construction, excepting for the feature thatit is strong enough to support at least two props in suspended position,forms Vno part of the present invention. This cap is disclosed in thecopending application Serial No. 189,114 of Karl Barall 3 and WilhelmWilkenloh to which reference may be had if necessary. The constructionof the cap 7 will be described only to the extent necessary for fullunderstanding of my present invention.

As best shown in FIG. 2, the cap 7 comprises four roof engaging membersor roof bars 8, 9, 10, 11 which assume the form of comparatively largemetallic plates and which are respectively secured to the upper portions6 of the props 1, 2, 3 and 4. The connections 12 between the roof bars 8to 11 and the respective upper prop portions 6 may assume the form ofconventional universal joints so that the roof bars are tiltable to acertain extent in all directions with respect to but remain connectedwith the portions 6. This is of advantage because the roof barsautomatically nd such positions of inclination in which they engagelarge surface areas of the mine roof 69 (see FIG. l) so that the loadstransmitted by the roof to the mine roof support cannot be concentratedin a few areas to cause deformation and eventual destruction of theapparatus.

The roof bars 8 to 11 are connected to each other by four specialcouplings including a rst pair of couplings 13, 14 which respectivelyconnect the roof bars S, 9 with the roof bars 10, 11 and a second pairof couplings 15, 16 which respectively connect the roof bars 8, with theroof bars 9, 11. The coupling 13 is shown in greater detail in FIG. l,and it will be noted that the component parts of this coupling arecarried by a pair of downwardly extending apertured connecting portionsor anges 17, 18 the former of which is integral with or secured to andis located at the rear end of the roof bar 8 and the latter of which isintegral with or secured to and is located at the forward end of theroof bar 10 so as to normally abut against the connecting portion 17when the composite cap 7 is caused to descend and does not engage themine roof 69. One of or both connecting portions 17, 18 are providedwith elongated preferably vertically extending slots 19 (see FIG. 3),for a bolt 20 which meshes with a nut 21 and which carries a pair ofwashers 22, 23 at the outer sides of the connecting portions 17, 18. Abiasing means in the form of a helical spring 24 is interposed between athird washer 74 (which engages the head of the bolt and the Washer 22 soas to normally bias the connecting portions 17, 18 into faceto-faceabutment with each other. Since the bolt 20 is slidable in thelongitudinal direction of the slots 19 and since the spring 24 yields toa certain pressure, the leading roof bar 8 may be moved to thephantom-line inclined position 8 of FIG. l or to the phantom =linelposition 8" of FIG. 3. the coupling 13 permits similar displacements ofthe roof bar 10 with respect to the roof bar 8. The strength of thespring 24 is selected in such a way that it can maintain the roof bar 8in the full-line position of FIG. 1 even if the drop 1 is caused tocontract so as to be suspended from the roof bar 8 and to lift a oorengaging element in the form of a sole plate 25 which is secured to itslower portion 5 above the mine iloor 26 as long as the prop 3 remainsextended in order to maintain the roof bar 10 and hence the roof bars 8,9 and 11 in supporting engagement with the mine roof 69.

The coupling 14 between the downwardly extending apertured connectingportion 27 at the rear end of the roof bar 9 and the downwardlyextending apertured connecting portion 28 at the forward end of the roofbar 11 is identical with the coupling 13 and, therefore, is indicatedonly schematically in FIG. 2 of the drawings.

The coupling 16 is shown in FIGS. 2 and 3, and it will be noted thatthis coupling is carried by a downwardly extending apertured connectingportion 29 which is provided along the inner longitudinal edge portionof the roof bar 10 and by a similar apertured connecting portion 30which is provided along the inner longitudinal edge portion of the roofbar 11. These connecting portions are formed with vertically extendingslots 19 to Of course, it will be readily understood that receive thebolt 20 of the coupling 16. All component parts of the coupling 16 areidentical with those described in connection with the coupling 13 andare identified by similar reference characters. The coupling 15 betweenthe apertured connecting portions 31, 32 of the respective leading roofbars S, 9 is identical with the coupling 16.

The roof bars 8, 9 are respectively provided with forwardly extendinglugs 33, 34 which are articulately connected with front shields 35, 36by means of horizontal pivot pins 37, 38. The tips of the lugs 33, 34are formed with downwardly and forwardly inclined cam faces which engagewith wedges 39 extending through arcuate apertures provided in therearwardly extending arms 41, 42 of the respective front shields. Insuch manner, the shields 35, 36 are maintained in supported engagementwith the mine roof 69 to prevent descent of rock or ore onto thecustomary conveyer 43 which is normally located in front of the leadingprops 1, 2 and which serves as a means for conveying the material whichis being removed from the mine face 44.

The rear `ends of the trailing roof bars 10, 11 are respectivelyconnected with rear shields 45, 46 whose purpose is to prevent the llingfrom descending into the area occupied by the mine roof support.

The manner in which the floor engaging sole plate 25 is secured to thelower portion 5 of the prop 1 is shown in FIG. l. The bottom part of theportion 5 is received in and is rigidly secured to a sleeve 50. Thissleeve is vertically reciprocably guided in a pair of spaced rings 51which are secured to an upwardly and forwardly inclined intermediateportion 52 of a slightly elastic Hoor contacting connecting plate ormain support 49 by means of cotter pins 53 or the like. The lower end ofthe sleeve forms a cup 54 which receives a ball 55 secured to the soleplate 25 so that the sleeve and the ball 55 together constitute a balland cup joint for the sole plate. The front portion 56 of the sole plateis bent upwardly whereby the latter resembles a runner and is capable ofpassing over protuberances in the mine floor 26. This front portion 56carries a pair of apertured brackets 57 (only one shown in FIG. l) for ahorizontal pin 58 secured to the lower end of a vertical bolt 59 whichis slidably guided in a pair of vertically spaced rings 60, the lattersecured to the rear side of a reinforcing plate or traverse 61. Thistraverse extends substantially to the level of the mine floor 26 and issecured to a box-like receptacle 62 which constitutes the foremost partof the connecting plate 49 and which extends forwardly of the portion 52and between the leading props 1 and 2. In addition to supporting therings 60, the traverse 61 also performs the function of a bulldozerblade or grader in that it evens out the mine floor 26 when the mineroof support is caused to advance toward the mine face 44. The extent towhich the bolt 59 may reciprocate in the rings 60 is determined by asecond horizontal pin 63 which is secured thereto at a point above theupper ring 60. The rings 51 and 60 enable the sole plate 25 toreciprocate with the prop 1 relative to the connecting plate 49 to theextent determined by the pins 75 on the sleeve 50 and the pins 58, 63 onthe bolt 59. In addition, the joints 54, enables the sole plate 25 tobecome tilted with respect to the prop 1 in order to move intolarge-area contact with an uneven mine floor.

The connection betwen the sole plate 64 (see FIG. 3) of the otherleading prop 2 and the connecting plate 49 is analogous and, therefore,is not shown in the drawings.

A third sole plate 65 is secured to a sleeve 50' on the lower portion 5forming part of the trailing prop 3 by means of a ball and cup joint55', 54 which is shown in FIG. l. The sleeve 50 is verticallyreciprocably guided in a pair of rings 51 which are secured to anupwardly and rearwardly inclined portion 66 of the connecting plate 49by means of cotter pins 53. The upwardly bent front portion 67 of thesole plate 65 carries a pair of brackets 57 for a horizontal pin 58which is secured to the lower end of a vertical bolt 59. This bolt isslidable in a pair of spaced rings 60 secured to the portion 66 of theconnecting plate 49. A horizontal pin 63' cooperates with the pin 58 tolimit axial movements of the bolt 59. The connection between a fourthsole plate and the lower portion of the second trailing prop 4 isanalogous and is not shown in the drawings.

The mine roof support may be advanced by means of a double-actinghydraulic cylinder 70 which extends between the props 1, 3 and 2, 4 inthe longitudinal direction of the apparatus and whose piston rod 71 iscoupled to the conveyor 43. The cylinder 70 extends through theaforementioned leading receptacle 62 and through a similar receptacle 68formed by the rear portion of the connecting plate 49 between thetrailing props 3 and 4. The connection between the cylinder 70 and thewalls of the leading receptacle 62 preferably assumes the form or" aCardan joint.

The exact construction of the sole plates, of the connecting plate 49,of the traverse 61 and of other parts shown in the lower part of FIG. lis disclosed in the copending patent application Serial No. 155,109 ofWilhelm Wilkenloh and Karl Barall to which reference may be had ifnecessary.

FIG. l further shows the manner in which the sole plates 25, 65 arelikely to penetrate into the material of the mine oor 26 when thecomposite cap 7 is in supporting engagement with the mine roof 69. Thesole plates form comparatively deep depressions 72, 73 and respectivelyassume the positions 65 which are shown in dotted lines.

FIG. 4 illustrates the leading pit prop 1, in axial section. The uppertubular portion 6 of this prop carries at its lower end an annularpiston 80 which is slidable in the lower portion 5. The lower end of thetubular portion 5 is Welded to a base plate 81 and, at its upper end,the portion 5 carries a sealing ring structure 82 which slidablyreceives the upper portion 6. The upper end of the portion 6 is securedto a header 83 which is provided with a pair of nipples 84, 85 connectedto conduits 79 leading to the pressure side of a pump 78 which drawspressure fluid from a source 77. The base plate 81 supports an internalcylinder 86 which extends with play through the piston 80 and whoseupper end is sealed by an annular end plate 87 which slidably receives ahollow piston rod 88, the latter secured at its upper end to the header83 and at its lower end to a second piston 89 which is slidably receivedin the internal cylinder 86. Adjacent to the piston S9, the piston rod88 is provided with ports 90 which permit communication of pressurefluid between the internal space 91 of the piston rod 88 and the upperchamber 92 in the cylinder 86, i.e. that chamber of this cylinder whichextends between the piston 89 and end plate 87. The lower chamber 93 ofthe tubular portion 5 communicates with the internal space 94 of theupper portion 6 through the annular clearance 95 between the peripheryof the cylinder 86 and the piston 80. The compartment 96 in the cylinder86 beneath the piston 89 communicates with the atmosphere through a bore97 provided in the base plate 81. It will be noted that the nipples 84,85 respectively communicate with the internal space 94 and with theinternal space 91. The part 98 of the tubular portion 6 above the header83 constitutes an element of the joint 12 between the prop 1 and roofbar 8.

In order to expand the prop 1 and to thereby move the roof bar 8 into rmsupporting engagement with the mine roof 69, the pressure side of thepump 78 is connected with the nipple 84 through a distributor valve 76whereby the pressure uid entering the space 94 and passing through theclearance 95 into the lower cylinder chamber 93 acts against theunderside of the piston 84) and expels the tubular portion 6 in upwarddirection. At the same time, uid contained in the upper cylinder chamber92 is permitted to flow through the ports 90, through the internal space91 and is discharged through the nipple 85, through the valve 76, andthrough a return line 79a. A pressure relief valve 76a in the conduitconnecting the nipple 84 with the pump 78 permits return llow ofpressure fluid through the line 79a and to the source 77 when the lluidpressure in the chamber 93 reaches a predetermined maximum value, i.e.when the tubular portion 6 has moved the roof bar 8 into satisfactorysupporting engagement with the mine roof.

The prop 1 contracts or collapses automatically if the operator connectsthe pump 7S with the nipple 85 and if the uid lling the chamber 93 ispermitted to escape through the nipple 84 and through the line 79a. Whenthe nipple admits pressure iluid, the fluid acts against the upper sideof the piston 89 and against the underside of the end plate 87 to movethe cylinder 86 and the tubular portion 5 upwardly, it being assumedthat the roof bar 8 remains in abutment with the mine roof 69 becausethe trailing props 3, 4 remain in expanded position. The tubular portion5 then lifts its sole plate from the phantom-line position 25 to thefull-line position 25 of FIG. 1 whereby the operator may till up thedepression 72 so that the sole plate 25 now rests on the material whichwas introduced into this depression. As stated before, it is oftenunnecessary to actually fill the depression 72 because it is filled byavalanching of material surrounding the sole plate 25.

The construction of the hydraulic expanding and contracting means in theprops 2, 3 and 4 is analogous to the construction of PIG. 4. As a rule,the operator will simultaneously contract the leading props 1, 2 whilethe trailing props 3, 4 remain in expanded position. The springs 24 ofthe couplings 13, 14 are strong enough to maintain the leading roof bars8, 9 in actual abutment with or close to the mine roof 69, i.e. thesprings 24 of the couplings 13, 14 are strong enough to maintain theleading props 1, 2 and their respective sole plates 25, 64 in suspendedposition as long as the trailing roof bars 10, 11 remain in rmsupporting engagement with the mine roof. Once the leading sole plates25, 64 come to rest on the material while now lls the respectivedepressions, the operator again admits pressure uid to the nipples 84 ofthe leading props 1, 2 so that these props expand and maintain theleading roof bars 8, 9 in engagement with the mine roof 69 while thetrailing props 3, 4 are caused to contract so that the operator oroperators may fill in the depressions which were formed by the trailingsole plates.

The mine roof support is advanced as follows:

Once the depressions formed by the foul sole plates are filled in, theoperator causes the leading and/or t-he trailing props to expand so thatthe respective roof bars engage the mine roof 69 and preventdisplacements of the cylinder 70. In the next step, fluid is admitted tothe rear chamber of the cylinder 70 in order to expel the piston rod 71and to move the conveyer 43 toward the mine face 44. The four props arethen caused to contract in order to move the composite cap 7 out ofactual engagement with the mine roof 69 and, as soon as pressure fluidis permitted to enter into the front chamber of the cylinder 70, theentire mine roof support is dragged toward the conveyer 43 until thepiston rod 71 is again withdrawn into the cylinder 70. The mine roofsupport is then ready to engage a new section of the mine roof.

The pump 78 which operates the hydraulic systems of the props 1 to 4 mayalso serve as a means for supplying pressure fluid to the cylinder 70.This pump is a stationary structure which is normally mounted in themine shaft to the rear of t-he mine roof support.

The purpose of the bore 97 is to prevent the compartment 96 fromdeveloping partial vacuum when the prop 1 expands and the piston 89moves in upward direction.

It will be readily understood that the hydraulic system for the props2-4 and for the cylinder 70 comprises a series of suitable pressurerelief and distributor valves and other auxiliaries which are usuallyaccommodated in a single valve block, not shown. This valve block may bemounted directly on the mine roof support or at a safe distancetherefrom.

It was found that it is often suicient to lift the leading sole plates25, 64 and thereupon the trailing sole plates for very short periods oftime, particularly if the depressions formed by the sole plates arecomparatively shallow. The self-filling action of comminuted materialsurrounding the depressions is almost instantaneous so that thetemporarily lifted props may be immediately reextended to move therespective sole plates into renewed contact with the mine floor.

Referring again to FIG. 4, it will be noted that, in normal operation(i.e. when the prop 1 is expanded), the chambers 92, 93 may remain underconstant pressure. In other words, the nipples 84, 85 may remainconnected simultaneously to the pressure side of the pump 78. Since theeffective surface of the piston 80 and base plate S1 is greater than theeffective surface of the parts 87, 89, the fluid filling the chamber 93will automatically retain the prop 1 in extended position. When theoperator wishes the prop to collapse, he merely disconnects the nipple84 from the pump 78 by operating the valve 76 or opens a suitable bypassvalve so that the fluid may escape from the chamber 93 whereby the fluidfilling the chamber 92 immediately lifts the tubular portion 5 in upwarddirection to reduce the overall length ofthe prop and to lift the soleplate 25 above the mine floor.

FIG. illustrates a portion of a greatly simplified mine roof supportwhich comprises only two pit props including a leading prop 100 and atrailing prop 101. These props are articulately connected with aone-piece cap 102 which assumes the form of a comparatively rigid plate.The manner in which the props 100, 101 are extensible and contractibleis the same as described in connection with FIG. 4. It is assumed thatthis mine roof support does not comprise an advancing cylinder such asthe cylinder 70 of the mine roof support shown in FIGS. 1 to 3.Therefore, the modified mine roof support must be advanced by anindependent advancing device of any known design which is not shown inthe drawings.

When the sole plate of the trailing prop 101 is in firm engagement withthe mine iloor and when the prop 101 is expanded, the cap 102 isautomatically retained in supporting engagement with the mine roof sothat the leading prop 100 may be caused to collapse and remainssuspended on the cap 102. In other words, here again,

the cap 102 must be strong enough to maintain the leading prop 100 insuspended position when the trailing prop is expanded, and vice versa.Once the depression formed by the sole plate of the prop 100 is filledup, the prop 100 is reextended and the operator then collapses thetrailing prop 101 in order to fill the depression formed by the trailingsole plate. It is necessary that the sole plates of the leading andtrailing props should have freedom of relative movement with respect toeach other to make sure that the leading sole plate or plates may belifted when the trailing sole plate or plates remain in engagement withthe mine floor, and vice versa. Of course, it will be readily understoodthat, owing to the provision of a four-piece cap 7, the mine roofsupport of FIGS. 1 to 3 may be brought to a position in which it isready to advance toward the mine face 44 by first lifting thelongitudinally aligned props 1, 3 and by thereupon lifting the similarlyaligned props 2, 4 or vice versa. In other words, it is not necessary tofirst suspend the leading props and thereupon the trailing props becausethe movability of roof bars 8, with respect to the roof bars 9, 11 issubstantially the same as the movability of roof bars 8, 9 with respectto the roof bars 10, 11.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by

applying knowledge, readily adapt it for various applications withoutomitting features that, from the standpoint of prior art, fairlyconstitute essential characteristics of the generic and specific aspectsof this invention and, therefore, such adaptations should and areintended to be comprehended within the meaning and range of equivalenceof the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A mine roof support comprising, in combination, two extensible andcontractible pit props each having two relatively movable portionsincluding an upper portion and a floor engaging lower portion; fluidoperated means operatively connected to said props for moving theportions of `said props with respect to each other; roof engaging capmeans comprising two articulately connected sections each secured to theupper portion of one of said props; and biasing means arranged to biasone of said sections in a direction toward the mine roof when the othersection engages the mine roof in response to extension of the respectiveprop, said biasing means being of such rigidity and strength that saidone section can support, without substantial turning relative to saidother section, the corresponding prop in suspended position when saidcorresponding prop is contracted to lift its lower portion above themine floor whereby any depressions formed by said lower portions in themine floor may be filled in -before the mine roof support is moved alongand while the lower portions of the props are alternately lifted abovethe mine floor.

2. A mine roof support as set forth in claim 1, wherein the fluidoperated means -comprises a single source of pressure fluid, said singlesource being arranged to supply pressure fluid for extending as well asfor contracting said props.

3. A mine roof support, as set forth in claim 1, wherein said propscomprise a plurality of relatively movable fluid containing cylinderswherein fluid is maintained at an elevated pressure.

4. A mine roof support as set forth in claim 1, wherein each of saidarticulately connected sections which form said roof engaging cap meansis articulately connected with the upper portion of one of said props.

5. A mine roof support as set forth in claim 4, wherein the biasingmeans are springs.

6. A mine roof support as set forth in claim 4, Wherein the articulateconnection between said sections comprises slotted connecting portionsprovided on said sections and adjacent to each other, bolt means looselyextending through said connecting porticns, and resilient means on saidbolt means for biasing said connecting portions into abutment with eachother.

7. A mobile mine roof support, comprising, in combination two extensibleand contractible pit props each having two relatively movable portionsincluding an upper portion and a lower portion; fluid operated meansoperatively connected to said props for moving the portions of saidprops with respect to each other; a floor contacting element provided onthe lower portion of each prop; roofengaging cap means comprising twoarticulately connected sections, each section secured to the upperportion of one of said props; resilient means arranged to bias one `ofsaid sections in a direction toward the mine roof when the other sectionengages the mine roof in response to extension of the respective prop,said biasing means being of such rigidity and strength that said onesection can support, without substantial turning relative to said othersection, the corresponding prop in suspended position when saidcorresponding prop is contracted to lift its lower portion above themine oor so that any depression formed in the mine floor by said floorcontacting elements may be filled in while the floor contacting elementsare lifted above the mine floor; a floor contacting main supportdisposed intermediate said floor contacting elements; and meansarticulately connecting said main support with said elements so thatsaid elements may be lifted while said main support remains in contactwith the mine oor.

8. A mobile mine roof support comprising, in combination, two extensibleand contractible pit props each having two relatively movable portionsincluding an 4upper portion and a lower portion; fluid operated meansoperatively connected to said props for moving the portions of saidprops with respect to each other; a floor contacting element provided onthe lower portion of each prop; roofengaging cap means comprising twoarticulately connectcd sections, each section secured to the upperportion of one of said props; resilient means arranged to bias one ofsaid sections in a direction toward the mine roof when the other sectionengages the mine roof in response to extension of the respective prop,said biasing means being of such rigidity and strength that said onesection can support, without substantial turning relative to said othersection, the corresponding prop in suspended position when saidcorresponding prop is contracted to lift its lower portion above themine floor so that any depressions formed in the mine oor by said floorcontacting elements may be lled up While the floor contacting elementsare lifted above the mine oor; a oor contacting main support disposedintermediate said floor contacting elements; means articulatelyconnecting said main support with said elements so that said elementsmay be lifted while the main support remains in contact with the minefloor; and ring means for vertically reciprocably receiving the lowerportions of said props, said ring means secured to said main support.

9. A mobile mine roo-f support comprising, in combination, twoextensible and contractible pit props each having two relatively movableportions including an upper portion and a lower portion; iluid operatedmeans operatively connected to said props for moving the portions ofsaid props with respect to each other; a iloor contacting elementprovided on the lower portion of each prop; roof-engaging cap meanscomprising two articullately connected sections, each section secured tothe upper portion of one of said props; resilient means arranged to biasone of said sections in a direction toward the mine roof when the othersection engages the mine roof in response to extension of the respectiveprop, said biasing means being of such rigidity and strength that saidone section can support, without substantial turning relative to saidother section, the corresponding prop in suspended position when saidcorresponding prop is contracted to lift its lower portion above themine iloor so that any depressions formed in the mine iioor by said oorcontacting elements may be filled in While the oor contacting elementsare lifted above the mine oor, each `of said lloor contacting elementshaving an upwardly bent front portion to facilitate its movements alongthe mine floor.

it?. A mobile mine roof support comprising, in combination, twoextensible and contractible pit props each having two relatively movableportions including an upper portion and a lower portion; fluid operatedmeans operatively connected to said props for moving the portions ofsaid props with respect to each other; a floor contacting elementprovided at the lower portion of each prop; universal jointsarticulately connecting said door contacting elements with therespective lower portions; roof-engaging cap means comprising twoarticulately connected sections, each section secured to the upperportion of one of said props, resilient means arranged to bias one ofsaid sections in a direction toward the mine roof when the other sectionengages the mine roof in response to extension of the respective prop,said biasing means being of such rigidity and strength that said onesection can support, without substantial turning relative to said othersection, the corresponding prop in suspended position when saidcorresponding prop is contracted to lift its lower portion above themine floor so that any depression formed in the mine floor by said Hoorcontacting elements may be lled in while the floor contacting elementsare lifted above the mine tloor.

References Cited by the Examiner UNITED STATES PATENTS 2,795,935 6/ 1957Fitzgerald 61-45.2 3,115,754 12/1963 Joseph 61-45 EARL I. WITMER,Primary Examiner. JACOB NACKENOFF, Examiner.

1. A MINE ROOF SUPPORT COMPRISING, IN COMBINATION, TWO EXTENSIBLE AND CONTRACTIBLE PIT PROPS EACH HAVING TWO RELATIVELY MOVABLE PORTIONS INCLUDING AN UPPER PORTION AND A FLOOR ENGAGING LOWER PORTION; FLUID OPERATED MEANS OPERATIVELY CONNECTED TO SAID PROPS FOR MOVING THE PORTIONS OF SAID PROPS WITH RESPECT TO EACH OTHER; ROOF ENGAGING CAP MEANS COMPRISING TWO ARTICULATELY CONNECTED SECTIONS EACH SECURED TO THE UPPER PORTION OF ONE OF SAID PROPS; AND BIASING MEANS ARRANGED TO BIAS ONE OF SAID SECTIONS IN A DIRECTION TOWARD THE MINE ROOF WHEN THE OTHER SECTION ENGAGES THE MINE ROOF IN RESPONSE TO EXTENSION OF THE RESPECTIVE PROP, SAID BIASING MEANS BEING OF SUCH RIGIDITY AND STRENGTH THAT SAID ONE SECTION CAN SUPPORT, WITHOUT SUBSTANTIAL TURNING RELATIVE TO SAID OTHER SECTION, THE CORRESPONDING PROP IN SUSPENDED POSITION WHEN SAID CORRESPONDING PROP IS CONTRACTED TO LIFT ITS LOWER PORTION ABOVE THE MINE FLOOR WHEREBY ANY DEPRESSIONS FORMED BY SAID LOWER PORTIONS IN THE MINE FLOOR MAY BE FILLED IN BEFORE THE MINE ROOF SUPPORT IS MOVED ALONG AND WHILE THE LOWER PORTIONS OF THE PROPS ARE ALTERNATELY LIFTED ABOVE THE MINE FLOOR. 